Heretofore, as a solar cell utilizing a Si semiconductor, one has been known wherein a semiconductor substrate having a n-type Si semiconductor layer formed on a light-receiving surface side of a p-type Si semiconductor layer is used, and on the light-receiving surface side of this semiconductor substrate, an antireflection layer is formed and a light-receiving surface electrode is also formed, and on the back surface side, a back surface electrode is formed.
The light-receiving surface electrode is formed as follows. That is, on a semiconductor substrate having an antireflection layer formed thereon, an electrically conductive paste comprising an electrically conductive silver powder, a glass frit and an organic vehicle is applied and baked to form a light-receiving surface electrode and to let it penetrate into the antireflection layer to electrically connect it to the semiconductor substrate, particularly to the n-type Si semiconductor layer.
As such a glass frit, one containing lead has been used. One containing lead has a relatively low melting point, and it is capable of sufficiently bonding the semiconductor substrate and the light-receiving surface electrode even when it is fired at a low temperature. However, lead is a hazardous substance, and therefore, one containing no lead is desired.
As a glass frit containing no lead, for example, one comprising from about 40 to 60 mol % of SiO2, from about 5 to 15 mol % of B2O3 and from about 5 to 20 mol % of Bi2O3 and further containing at least one member selected from the group consisting of Al2O3, TiO2, CuO, CaO, BaO, ZnO and ZrO2, has been known (e.g. Patent Document 1).
Further, for example, one comprising from 0.1 to 8 wt % of SiO2, from 8 to 25 wt % of B2O3 and from 28 to 85 wt % of Bi2O3 and further containing from 0 to 4 wt % of Al2O3, from 0 to 1 wt % of CaO, from 0 to 42 wt % of ZnO, from 0 to 4 wt % of Na2O, from 0 to 3.5 wt % of Li2O, from 0 to 3 wt % of Ag2O, from 0 to 4.5 wt % of Ce2O, from 0 to 3.5 wt % of SnO2 and from 0 to 15 wt % of BiF3, has been known (e.g. Patent Document 2).